<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
  <style>
    .box {
      margin: 50px auto;
      width: 500px;
      height: 200px;
      background-color: pink;
        /*保证盒子是长方形，取值高度的一半*/
        border-radius: 100px;
    }
  </style>
</head>
<body>
  <div class="box"></div>
</body>
</html>